1. Field of the Invention
The present invention relates to a phthalocyanine composition having diffraction peaks at 7.0xc2x0, 9.0xc2x0, 14.1xc2x0, 18.0xc2x0, 23.7xc2x0 and 27.3xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum with a 1.541 xc3x85 X-ray of Cu Kxcex1, a phthalocyanine composition having diffraction peaks at 7.0xc2x0, 9.3xc2x0, 10.5xc2x0, 13.1xc2x0, 20.6xc2x0, 23.7xc2x0, 26.2xc2x0 and 27.2xc2x0 of Bragg angles, and an oxytitanium phthalocyanine having diffraction peaks at 7.5xc2x0, 10.2xc2x0, 16.3xc2x0, 22.5xc2x0, 24.2xc2x0, 25.4xc2x0, 27.2xc2x0 and 28.7xc2x0 of Bragg angles, wherein the intensity of peak at 7.5xc2x0 of a Bragg angle is the strongest among the above peaks. It also relates to a process for producing the same and to an electrophotographic photoreceptor using the same.
2. Prior Art
In recent years, the utilization of an electrophotography has not been limited to the field of a copying machine, but has spread in fields of a conventional photography, for example, the field of a printing plate material, a slide film or a microfilm. In addition, the application thereof has been also studied in the field of a high-speed printer using a laser, LED or CRT as a light source. Further, the application thereof has been lately directed to the use of a photoconductive material other than an electrophotographic photoreceptor, for example, the use of an electrostatic recording element, a sensor material or an EL element. Therefore, demands for a photoconductive material and an electrophotographic photoreceptor using the same have been increasing and become high level.
As the conventional photoreceptor of an electrophotography, an inorganic photoconductive substance, such as selenium, cadmium sulfide, zinc oxide or silicon, has been known, widely studied and already used practically. An inorganic substance has various problems although it has a number of advantages. For example, selenium has problems in that it is difficult to optimize production conditions thereof and it is easily crystallized due to heat and mechanical impact. Cadmium sulfide and zinc oxide have poor resistance to humidity and durability. It is pointed out that silicon has a poor electrostatic chargeability and is difficult to be produced. Further, selenium and cadmium sulfide also have problems on toxicity.
On the other hand, an organic photoconductive substance is advantageous in that it has an excellent film-formability and flexibility as well as in that it is lightweight and has an excellent transparency. Further, it also has advantages in that a photoreceptor to be used in a wide range of wavelength is easily designed therefrom by using an appropriate sensitization method. Therefore, attention is now drawn to the practical use of an organic photoconductive substance.
By the way, the photoreceptor used in the electrophotography is necessary to meet, as general basic properties, the following requirements: (1) that the electrostatic chargeability for the corona discharge in darkness be high; (2) that the leakage in darkness (dark decay) of the obtained electric charge be small; (3) that the dissipation (light decay) of the electric charge by light irradiation be rapid; and (4) that the residual electric charge after light irradiation be small.
A number of studies have been made on photoconductive polymers as organic photoconductive substances, including polyvinyl carobazole as of today. However, they do not necessarily have satisfactory film-formability, flexibility and adhesion property. Further, they do not have the above-mentioned basic properties required for a photoreceptor satisfactorily.
On the other hand, an organic photoconductive compound having a low molecular weight is advantageous in that a photoreceptor having an excellent film-formability, an excellent adhesion property and a high mechanical strength, such as flexibility, can be obtained by appropriately selecting a binder used in the photoreceptor formation. However, it is difficult to find an appropriate compound suitable to maintain high sensitivity.
For improving such properties, an organic photoreceptor having higher sensitivity has been developed in which different substances individually have a charge generation function and a charge transportation function. The characteristic feature of such a photoreceptor, which is called xe2x80x9cfunction separation typexe2x80x9d, resides in that it is possible to select materials suitable for the respective functions from wide varieties. Therefor, a photoreceptor having desired performance can be easily prepared, which have led to a number of researches on the photoreceptor.
As substances responsible for the charge generation function, various substances, such as a phthalocyanine pigment, a squarilium dye, an azo-pigment and a perylene pigment, have been studied. Among them, an azo-pigment is advantageous not only in that it is possible to prepare those having various molecular structures, but also in that a high charge generation efficiency is expected. Therefore, various azo-pigments has been widely researched and put into practical use. However, a relationship between the molecular structure and the charge generation efficiency in the azo-pigment has not yet been elucidated. Currently, although an enormous number of researches have been made on the synthesis of the azo-pigment having an optimum molecular structure, the satisfactory photoreceptor meeting the requirements of the above-mentioned basic properties and high durability has not yet been obtained.
Further, in recent years, according to the progress of information technology, laser beam printers using a laser as a light source instead of the conventional white light have been rapidly and widely expanded since they have advantages of high speed, high image quality and non-impact. In accordance with the expansion, it is desired to develop materials for such printers, which meet the demands for high performance of the printers. Among lasers, especially in a semiconductor laser, the use thereof in a compact disk or an optical disk is recently increased, and thus, the technical advance has been remarkably progressed. Therefore, the semiconductor laser has been vigorously used also in a printer field as a light source material being compact and high reliability. In such a case, the wave-length of the light source is about 780 to 830 nm, and therefore, it is strongly desired to develop a photoreceptor having high sensitivity in a near infrared range. Especially, a photoreceptor using a phthalocyanine with an optical absorption in a near infrared range is energetically developed.
It has been known that phthalocyanines have the different absorption spectrum and photoconductivity depending on the type of the central metal, and, in addition, among phthalocyanines having the same central metal, the properties of such phthalocyanines are different from each other according to the crystal structure thereof. Therefor, a phthalocyanine having a specific crystal structure is selected as an electrophotographic photoreceptor.
Taking as an example an oxytitanium phthalocyanine (hereinafter, referred to as xe2x80x9cTiOPcxe2x80x9d), an xcex1-TiOPc, which has main diffraction peaks at 7.6xc2x0, 10.2xc2x0, 22.3xc2x0, 25.3xc2x0 and 28.6xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum, has been described in Japanese Unexamined Patent Publication No. 217050/1986. A xcex2-TiOPc, which has main diffraction peaks at 9.3xc2x0, 10.6xc2x0, 13.2xc2x0, 15.1xc2x0, 15.7xc2x0, 16.1xc2x0, 20.8xc2x0, 23.3xc2x0, 26.3xc2x0 and 27.1xc2x0 of Bragg angles, has also been described in Japanese Unexamined Patent Publication No. 67094/1987. However, both of them do not satisfy the required high properties satisfactorily.
Among the TiOPc""s having a peak at 27.2xc2x0 of a Bragg angle, a II-TiOPc described in the above publication has a poor electrostatic chargeability and a low sensitivity. In Japanese Unexamined Patent Publication No. 17066/1989, a Y-TiOPc having a relatively high sensitivity with main diffraction peaks at 9.5xc2x0, 9.7xc2x0, 11.7xc2x0, 15.0xc2x0, 23.5xc2x0, 24.1xc2x0 and 27.3xc2x0 of Bragg angles is described. However, this TiOPc has problems in that the crystal structure thereof transforms easily to another crystal structure during dispersion, and the dispersion thereof has a poor stability with time.
In addition, it has been described that a mixed crystal comprising two or more different phthalocyanines or a mixture obtained simply by mixing together two or more different phthalocyanines is used as a charge generating material in an electrophotographic photoreceptor. For example, an xcex1-TiOPc composition comprising an xcex1-TiOPc and a metal-free phthalocyanine (hereinafter, referred to as xe2x80x9cH2Pcxe2x80x9d), described in Japanese Unexamined Patent Publications No. 142659/1989 and No. 221461/1989, has a poor maintaining ratio for electric charge and does not have a satisfactory sensitivity. The mixed crystal comprising two or more phthalocyanines having different central metals, described in Japanese Unexamined Patent Publication No. 170166/1990, exhibits a totally different X-ray diffraction spectrum from that of the present invention, resulting in unsatisfactory electrophotographic characteristics. The phthalocyanine crystal described in Japanese Unexamined Patent Publication No. 9962/1991 has different peaks in an infrared (IR) spectrum from those of the present invention, resulting in an unsatisfactory sensitivity. As described in Japanese Unexamined Patent Publication No. 255456/1991, the mixture obtained simply by mixing together a TiOPc, which has diffraction peaks at 9.0xc2x0, 14.2xc2x0, 23.9xc2x0 and 27.1xc2x0 of Bragg angles, or a TiOPc, which has diffraction peaks at 7.4xc2x0, 9.2xc2x0, 10.4xc2x0, 11.6xc2x0, 13.0xc2x0, 14.3xc2x0, 15.0xc2x0, 23.4xc2x0, 24.1xc2x0, 26.2xc2x0 and 27.2xc2x0 of Bragg angles, and a H2Pc has a poor electrostatic chargeability, resulting in an unsatisfactory sensitivity. Further, when a dispersion of this mixture is allowed to stand, precipitation of a crystal is observed. In Japanese Unexamined Patent Publication No. 110649/1996, a mixed crystal of a TiOPc, which has main diffraction peaks at 6.8xc2x0, 7.4xc2x0, 15.0xc2x0, 24.7xc2x0, 26.2xc2x0 and 27.2xc2x0 of Bragg angles, and a H2Pc is described. The mixed crystal exhibits a different X-ray diffraction spectrum from that of the present invention and does not have the properties required.
As mentioned above, with respect to the preparation of an electrophotographic photoreceptor, various improvements have been made; however, those which satisfy the requirements including the above-mentioned basic properties required for the photoreceptor, a high durability and the like have not yet been obtained.
An object of the present invention is to provide an electrophotographic photoreceptor having high charge potential and high sensitivity as well as excellent performance without changing in properties thereof even when it is used repeatedly. It is also to provide a phthalocyanine composition used in the electrophotographic photoreceptor.
The present inventors have made extensive and intensive studies with a view toward attaining the above object. As a result, it has been found that by conducting a crystal transformation using water and an aromatic compound or by conducting a treatment in the presence of a xcex2-TiOPc, a phthalocyanine with excellent electrophotographic characteristics can be obtained.
A phthalocyanine composition of the present invention comprises an oxytitanium phthalocyanine and a metal-free phthalocyanine, wherein said composition has diffraction peaks at 7.0xc2x0, 9.0xc2x0, 14.1xc2x0, 18.0xc2x0, 23.7xc2x0 and 27.3xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum with a 1.541 xc3x85 X-ray of Cu Kxcex1.
A process for producing a phthalocyanine composition of the present invention comprises subjecting an amorphous phthalocyanine composition comprising an oxytitanium phthalocyanine and a metal-free phthalocyanine to a treatment in a solvent containing water and an aromatic compound, to thereby effect the transformation to a crystal structure, which has diffraction peaks at 7.0xc2x0, 9.0xc2x0, 14.1xc2x0, 18.0xc2x0, 23.7xc2x0 and 27.3xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum with a 1.541 xc3x85 X-ray of Cu Kxcex1.
A phthalocyanine composition of the present invention comprises an oxytitanium phthalocyanine and a metal-free phthalocyanine, which has diffraction peaks at 7.0xc2x0, 9.3xc2x0, 10.5xc2x0, 13.1xc2x0, 20.6xc2x0, 23.7xc2x0, 26.2xc2x0 and 27.2xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum with a 1.541 xc3x85 X-ray of Cu Kxcex1.
An oxytitanium phthalocyanine of the present invention is obtained by allowing an amorphous oxytitanium phthalocyanine to transform to a crystal structure, which has diffraction peaks at 7.5xc2x0, 10.2xc2x0, 16.3xc2x0, 22.5xc2x0, 24.2xc2x0, 25.4xc2x0, 27.2xc2x0 and 28.7xc2x0 of Bragg angles (2xcex8xc2x10.2xc2x0) in an X-ray diffraction spectrum with a 1.541 xc3x85 X-ray of Cu Kxcex1, wherein the intensity of peak at 7.5xc2x0 of a Bragg angle (2xcex8xc2x10.2xc2x0) is strongest among the above peaks.